An image display device that modulates illumination light emitted from a light source device to form an image in response to image information and enlarges and projects the image onto a projection surface such as a screen has been conventionally known (e.g., see PTL 1).
The image display device disclosed in PTL 1 includes an illumination device, a polarization separation device, a spectroscopic device, liquid crystal panels, a prism, and a projection optical device. The illumination device includes an excitation light source that emits excitation light, and a phosphor. The phosphor converts a portion of incident excitation light to fluorescence at a wavelength different from the excitation light. The fluorescence and another portion of the excitation light are emitted as illumination light from the phosphor toward the same side as the side on which the excitation light is incident. The spectroscopic device includes two dichroic mirrors. A first dichroic mirror separates blue light from the illumination light, and a second dichroic mirror separates red light and green light therefrom. These separated color lights are modulated by the liquid crystal panels respectively corresponding thereto. Then, the color lights modulated by the liquid crystal panels are combined by the prism and projected from the projection optical device.